Consider:
1 - Vitamin D supports the creation of thyroid hormone, and of the major antidepressant neurotransmitters, serotonin, dopamine and norepinephrine; and it helps with calcium use; altogether suggesting antidepressant activity. And that is just what researchers are reporting. (See, for instance, Vieth 2004, Gloth 1999, Landsdowne 1998)Thus, D seems to be antidepressant, so is potentially promanic. See previous entry, Therapeutic Moderation, & Attention to Causes

2- Vitamin D is created by the interaction of sunlight with skin. Levels typically increase about 50% over the year, from approximately 16 ng/mL in winter to 24 in the summer. Vieth 2004
Schneider 2000 found levels in depressives at 80% that of normals.If the continuum holds, manics would have above-normal levels.

Question is, especially in those bipolars prone to mania as hours of sun increase, does several thousand IU of supplemental D, at a time when body levels are already rising, further fuel those manias... making temporary intake reductions advisable?